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A Chandra Survey of Early-Type Galaxies. I. Metal Enrichment in the Interstellar Medium
We present a Chandra study of the emission-weighted metal abundances in28 early-type galaxies, spanning ~3 orders of magnitude in X-rayluminosity (LX). We report constraints for Fe, O, Ne, Mg, Si,S, and Ni. We find no evidence of the very subsolar Fe abundance(ZFe) historically reported, confirming a trend in recentobservations of bright galaxies and groups, nor do we find anycorrelation between ZFe and luminosity. Excepting one case,the ISM is single-phase, indicating that multitemperature fits foundwith ASCA reflected temperature gradients that we resolve with Chandra.We find no evidence that ZFe (ISM) is substantially lowerthan the stellar metallicity estimated from simple stellar populationmodels. In general, these quantities are similar, which is inconsistentwith galactic wind models and recent hierarchical chemical enrichmentsimulations. Our abundance ratio constraints imply that 66%+/-11% of theISM Fe was produced in SNe Ia, similar to the solar neighborhood,indicating similar enrichment histories for elliptical galaxies and theMilky Way. Although these values are sensitive to the considerablesystematic uncertainty in the supernova yields, they are in agreementwith observations of more massive systems. This indicates considerablehomology in the enrichment process operating from cluster scales tolow-to-intermediate-LX galaxies. The data uniformly exhibitlow ZO/ZMg ratios, which have been reported insome clusters, groups, and galaxies. This is inconsistent with standardSN II metal yield calculations and may indicate an additional source ofenrichment, such as Population III hypernovae.
| Velocity Dispersion, Mass, and the Luminosity Function of the Fossil Cluster RX J1416.4+2315
We study the properties of the fossil cluster RX J1416.4+2315 throughg'- and i'-band imaging and spectroscopy of 25 member galaxies. Thesystem is at a mean redshift of 0.137 and has a velocity dispersion of584 km s-1. Superposed onto one quadrant of the cluster fieldis a group of five galaxies at a mean redshift of 0.131, which, ifincluded as part of the cluster, increases the velocity dispersion to846 km s-1. The central object of RX J1416.4+2315 is a normalelliptical galaxy with no cD envelope. The luminosity function of thesystem, estimated by the number counts and statistical backgroundcorrection in the range -22.6
| The Luminosity Function of the Fossil Group RX J1552.2+2013
We determine the first fossil group luminosity function based onspectroscopy of the member galaxies. The fossil group RX J1552.2+2013has 36 confirmed members, is at a mean redshift of 0.136, and has avelocity dispersion of 623 km s-1 (or 797 km s-1if four emission-line galaxies in the outskirts of the velocitydistribution are included). The luminosity function of RX J1552.2+2013,measured within the inner region of the system (~1/3Rvir) inthe range -23.5
| The fundamental plane of isolated early-type galaxies
Here we present new measurements of effective radii, surfacebrightnesses and internal velocity dispersions for 23 isolatedearly-type galaxies. The photometric properties are derived from newmulticolour imaging of ten galaxies, whereas the central kinematics forseven galaxies are taken from forthcoming work by Hau & Forbes.These are supplemented with data from the literature. We reproduce thecolour-magnitude and Kormendy relations and strengthen the result of therecent work of Reda et al. that isolated galaxies follow the samephotometric relations as galaxies in high-density environments. We alsofind that some isolated galaxies reveal fine structure indicative of arecent merger, while others appear undisturbed. We examine theFundamental Plane both in the traditional Re,μe, σ space and also in κ space. Most isolatedgalaxies follow the same Fundamental Plane tilt and scatter for galaxiesin high-density environments. However, a few galaxies notably deviatefrom the Plane in the sense of having smaller M/L ratios. This can beunderstood in terms of their younger stellar populations, which arepresumably induced by a gaseous merger. Overall, isolated galaxies havesimilar properties to those in groups and clusters with a slightenhancement in the frequency of recent mergers/interactions.
| Group, field and isolated early-type galaxies - II. Global trends from nuclear data
We have derived ages, metallicities and enhanced-element ratios[α/Fe] for a sample of 83 early-type galaxies essentially ingroups, the field or isolated objects. The stellar-population propertiesderived for each galaxy correspond to the nuclear re/8aperture extraction. The median age found for Es is 5.8+/-0.6 Gyr andthe average metallicity is +0.37+/-0.03 dex. For S0s, the median age is3.0+/-0.6 Gyr and [Z/H]= 0.53+/-0.04 dex. We compare the distribution ofour galaxies in the Hβ-[MgFe] diagram with Fornax galaxies. Ourelliptical galaxies are 3-4 Gyr younger than Es in the Fornax cluster.We find that the galaxies lie in a plane defined by [Z/H]= 0.99logσ0- 0.46 log(age) - 1.60, or in linear terms Z~σ0× (age) -0.5. More massive (largerσ0) and older galaxies present, on average, large[α/Fe] values, and therefore must have undergone shorterstar-formation time-scales. Comparing group against field/isolatedgalaxies, it is not clear that environment plays an important role indetermining their stellar-population history. In particular, ourisolated galaxies show ages differing by more than 8 Gyr. Finally weexplore our large spectral coverage to derive log(O/H) metallicity fromthe Hα and NIIλ6584 and compare it with model-dependent[Z/H]. We find that the O/H abundances are similar for all galaxies, andwe can interpret it as if most chemical evolution has already finishedin these galaxies.
| Group, field and isolated early-type galaxies - I. Observations and nuclear data
This is the first paper of a series on the investigation of stellarpopulation properties and galaxy evolution of an observationallyhomogeneous sample of early-type galaxies in groups, field and isolatedgalaxies.Here we present high signal-to-noise ratio (S/N) long-slit spectroscopyof 86 nearby elliptical and S0 galaxies. Eight of them are isolated,selected according to a rigorous criterion, which guarantees a genuinelow-density subsample. The present survey has the advantage of coveringa larger wavelength range than normally found in the literature, whichincludes [OIII]λ5007 and Hα, both lines important foremission correction. Among the 86 galaxies with S/N >= 15 (perresolution element, for re/8 central aperture), 57 have theirHβ-index corrected for emission (the average correction is 0.190Åin Hβ) and 42 galaxies reveal [OIII]λ5007 emission,of which 16 also show obvious Hα emission. Most of the galaxies inthe sample do not show obvious signs of disturbances nor tidal featuresin the morphologies, although 11 belong to the Arp catalogue of peculiargalaxies; only three of them (NGC 750, 751 and 3226) seem to be stronglyinteracting. We present the measurement of 25 central line-strengthindices calibrated to the Lick/IDS system. Kinematic information isobtained for the sample. We analyse the line-strength index versusvelocity dispersion relations for our sample of mainly low-densityenvironment galaxies, and compare the slope of the relations withcluster galaxies from the literature. Our main findings are that theindex-σ0 relations presented for low-density regionsare not significantly different from those of cluster E/S0s. The slopeof the index-σ0 relations does not seem to change forearly-type galaxies of different environmental densities, but thescatter of the relations seems larger for group, field and isolatedgalaxies than for cluster galaxies.
| Baryonically Closed Galaxy Groups
Elliptical galaxies and their groups having the largestLX/LB lie close to the locus LX = 4.3× 1043(LB/1011LB,solar)1.75 expected for closed systems havingbaryon fractions equal to the cosmic mean value, fb~0.16. Theestimated baryon fractions for several of these galaxies/groups are alsoclose to fb=0.16 when the gas density is extrapolated to thevirial radius. Evidently they are the least massive baryonically closedsystems. Gas retention in these groups implies that nongravitationalheating cannot exceed about 1 keV per particle, consistent with theheating required to produce the deviation of groups from theLX-T correlation for more massive clusters. Isolatedgalaxies/groups with X-ray luminosities significantly lower thanbaryonically closed groups may have undermassive dark halos, overactivecentral AGNs, or higher star formation efficiencies. The virial mass andhot gas temperatures of nearly or completely closed groups correlatewith the group X-ray luminosities and the optical luminosities of thegroup-centered elliptical galaxy, i.e.,Mvir~L1.33B, an expected consequence oftheir merging history. The ratio of halo mass to the mass of the centralgalaxy for X-ray-luminous galaxies/groups isMvir/M*~80.
| Testing galaxy evolution in the field: morphology and properties of the diffuse X-ray emission in shell galaxies.
Not Available
| Small-Scale Systems of Galaxies. II. Properties of the NGC 4756 Group of Galaxies
This paper is part of a series that focuses on investigating galaxyformation and evolution in small-scale systems of galaxies inlow-density environments. We present results from a study of the NGC4756 group, which is dominated by the elliptical galaxy NGC 4756. Thecharacteristics of the group are investigated through (1) the detailedinvestigation of the morphological, photometric, and spectroscopicproperties of nine galaxies among the dominant members of the group; (2)the determination of the photometric parameters of the faint galaxypopulation in an area of 34'×34' centered onNGC 4756 and (3) an analysis of the X-ray emission in the area based onarchival data.The nine member galaxies are located in the core part of the NGC 4756group (a strip ~300 kpc in diameter, H0=70 km s-1Mpc-1), which has a very loose configuration. The centralpart of the NGC 4756 group contains a significant fraction of early-typegalaxies. Three new group members with previously unknown systemicvelocities are identified, one of which is type dE. At about 7.5 arcminsouthwest of NGC 4756 a substructure of the group is detected, includingIC 829, MCG -2-33-35, MCG -2-33-36, and MCG -2-33-38, that meets theHickson criteria for being a compact group. Most of the galaxies in thissubstructure show interaction signatures. We do not detect apparent finestructure and signatures of recent interaction events in the early-typegalaxy population, with the exception of a strong dust lane in theelliptical galaxy MCG -2-33-38. However, this galaxy displays signaturesof nuclear activity. Strong [O III], [N II], and [S II] line emission,combined with comparatively weak but broad Hα emission, suggestsan intermediate Seyfert type classification. Although the area isheavily contaminated by the background cluster A1631, X-ray data suggestthe presence of a hot intergalactic medium related to the detected X-rayemission of the group. The present results are discussed in the contextof group evolution.Based on observations obtained at the European Southern Observatory, LaSilla, Chile (program 65.P-252).
| A wide-field photometric study of the globular cluster system of NGC 4636
Previous smaller-scale studies of the globular cluster system of NGC4636, an elliptical galaxy in the southern part of the Virgo cluster,have revealed an unusually rich globular cluster system. Were-investigate the cluster system of NGC 4636 with wide-field Washingtonphotometry. The globular cluster luminosity function can be followedroughly 1 mag beyond the turn-over magnitude found at {V} =23.31±0.13 for the blue cluster sub-population. This correspondsto a distance modulus of ({m}-{M})=31.24±0.17, 0.4 mag largerthan the distance determined from surface brightness fluctuations. Thehigh specific frequency is confirmed, yet the exact value remainsuncertain because of the uncertain distance: it varies between5.6±1.2 and 8.9±1.2. The globular cluster system has aclearly bimodal color distribution. The color peak positions show noradial dependence and are in good agreement with the values found forother galaxies studied in the same filter system. However, a luminositydependence is found: brighter clusters with an“intermediate” color exist. The clusters exhibit a shallowradial distribution within 7´, represented by a power-law with anexponent of -1.4. Within the same radial interval, the galaxy light hasa distinctly steeper profile. Because of the difference in the clusterand light distribution the specific frequency increases considerablywith radius. At 7´ and 9´ the density profiles of the redand blue clusters, respectively, change strongly: the power-law indicesdecrease to around -5 and become similar to the galaxy profile. Thissteep profile indicates that we reach the outer rim of the clustersystem at approximately 11´. This interpretation is supported bythe fact that in particular the density distribution of the blue clusterpopulation can be well fit by the projection of a truncated power-lawmodel with a core. This feature is seen for the first time in a globularcluster system. While the radial distribution of the cluster and fieldpopulations are rather different, this is not true for the ellipticityof the system: the elongation as well as the position angle of thecluster system agree well with the galaxy light. We compare the radialdistribution of globular clusters with the light profiles for a sampleof elliptical galaxies. The difference observed in NGC 4636 is typicalof an elliptical galaxy of this luminosity. The intrinsic specificfrequency of the blue population is considerably larger than that of thered one.Tables A.1 to A.6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/433/43
| A catalogue of ultraluminous X-ray sources in external galaxies
We present a catalogue of ultraluminous X-ray sources (ULXs) in externalgalaxies. The aim of this catalogue is to provide easy access to theproperties of ULXs, their possible counterparts at other wavelengths(optical, IR, and radio), and their host galaxies. The cataloguecontains 229 ULXs reported in the literature until April 2004. Most ULXsare stellar-mass-black hole X-ray binaries, but it is not excluded thatsome ULXs could be intermediate-mass black holes. A small fraction ofthe candidate ULXs may be background Active Galactic Nuclei (AGN) andSupernova Remnants (SNRs). ULXs with luminosity above 1040ergs s-1 are found in both starburst galaxies and in thehalos of early-type galaxies.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/429/1125
| The photometric properties of isolated early-type galaxies
Isolated galaxies are important because they probe the lowest densityregimes inhabited by galaxies. We define a sample of 36 nearby isolatedearly-type galaxies for further study. Our isolation criteria requirethem to have no comparable-mass neighbours within 2 B-band magnitudes,0.67 Mpc in the plane of the sky and 700 km s-1 in recessionvelocity. New wide-field optical imaging of 10 isolated galaxies withthe Anglo-Australian Telescope confirms their early-type morphology andrelative isolation. We also present imaging of four galaxy groups as acontrol sample. The isolated galaxies are shown to be moregravitationally isolated than the group galaxies. We find that theisolated early-type galaxies have a mean effective colour of(B-R)e= 1.54 +/- 0.14, similar to their high-densitycounterparts. They reveal a similar colour-magnitude relation slope andsmall intrinsic scatter to cluster ellipticals. They also follow theKormendy relation of surface brightness versus size for luminous clustergalaxies. Such properties suggest that the isolated galaxies formed at asimilar epoch to cluster galaxies, such that the bulk of their stars arevery old. However, our galaxy modelling reveals evidence for dust lanes,plumes, shells, boxy and disc isophotes in four out of nine galaxies.Thus at least some isolated galaxies have experienced a recentmerger/accretion event, which may have induced a small burst of starformation. We derive luminosity functions for the isolated galaxies andfind a faint slope of -1.2, which is similar to the `universal' slopefound in a wide variety of environments. We examine the number densitydistribution of galaxies in the field of the isolated galaxies. Only thevery faintest dwarf galaxies (MR>~-15.5) appear to beassociated with the isolated galaxies, whereas anyintermediate-luminosity galaxies appear to lie in the background.Finally, we discuss possible formation scenarios for isolated early-typegalaxies. Early epoch formation and a merger/accretion of galaxies arepossible explanations. The collapse of a large, virialized group is anunlikely explanation, but that of a poor group remains viable.
| The Halo Mass Distribution of Field and Cluster Early-Type Galaxies
We describe an ongoing program to study the halo kinematics of a broadsample of early-type galaxies using integrated light measurementsobtained with the Hobby-Eberly and Gemini Telescopes.The Hobby-Eberly Telescope is operated by McDonald Observatory on behalfof the University of Texas at Austin, The Pennsylvania State University,Stanford University, Ludwid-Maximilians-Universit at Munchen, andGeorg-August-Universitat Gottingen.Part of this project is based on observations obtained at the GeminiObservatory, which is operated by AURA, INC., under a cooperativeagreement with the NSF on behalf of the Gemini Partnership: The NSF(USA), PPARC (UK), NRC (Canada), CONICYT (Chile), ARC (Australia), CNPq(Brazil) and CONICET (Argentina ).
| Early-Type Galaxies in Extremely Isolated Environments: Typical Ellipticals?
We have conducted a BVR imaging survey of nine early-type galaxiespreviously verified to exist in extremely isolated environments. Ourgoals are to establish a baseline of morphological and photometricproperties for spheroidal systems evolving in extremely low-densityenvironments and to compare these properties with signatures predictedfor merged galaxy groups. We find that these isolated systems areunderluminous by at least a magnitude compared with objects identifiedas merged group remnants in other studies. Image processing techniquessensitive to shell features produced no detections, a result in strongcontrast to the high frequency of such structures found in otherisolated elliptical galaxies. Two objects, KIG 164 and KIG 870, appearto be merger remnants, as indicated by their disturbed morphology,apparent tidal features, and blue colors. KIG 164 exhibits an asymmetricnuclear morphology and a low surface brightness ``bridge'' between itand a possible dwarf satellite. KIG 870 shows both fan-shaped emissionat large radii and a possible double nucleus. Two other galaxies, KIG412 and KIG 792, are also blue, but without any morphologicalpeculiarities, suggesting that these systems are advanced mergers, olderthan KIG 164 and KIG 870. Two systems appear to be isolated lenticulargalaxies with no evidence of a merger history. Based on their redcolors, good fit to a R1/4-law light distribution, and thelack of morphological peculiarities, two other galaxies, KIG 557 and KIG824, are found to be excellent candidates for passively evolvingprimordial elliptical galaxies formed early in cosmic time. Optical datawere obtained with the 2.1 m Otto Struve telescope at McDonaldObservatory, which is operated by the University of Texas at Austin.
| Very Isolated Early-Type Galaxies
We use the Karachentseva Catalogue of Very Isolated Galaxies toinvestigate a candidate list of more than 100 very isolated early-typegalaxies. Broadband imaging and low-resolution spectroscopy areavailable for a large fraction of these candidates and result in asample of 102 very isolated early-type galaxies, including 65 elliptical(E) and 37 S0 galaxies. Many of these systems are quite luminous, andthe resulting optical luminosity functions of the E and early-type(E+S0) galaxies show no statistical differences when compared toluminosity functions dominated by group and cluster galaxies. However,whereas S0 galaxies outnumber E galaxies 4:1 in the CfA survey, isolatedE outnumber S0 galaxies by nearly 2:1. We conclude that very isolatedelliptical galaxies show no evidence of a different formation and/orevolution process compared to those formed in groups or clusters, butthat most S0 galaxies are formed by a mechanism (e.g., gas stripping)that occurs only in groups and rich clusters. Our luminosity functionresults for elliptical galaxies are consistent with very isolatedelliptical galaxies being formed by merger events, in which nocompanions remain. Chandra observations were proposed specifically totest the merger hypothesis for isolated elliptical galaxies. However,this program has resulted in the observation of only one isolatedearly-type galaxy, the S0 KIG 284, which was not detected at a limitwell below that expected for a remnant group of galaxies. Therefore, thehypothesis remains untested that very isolated elliptical galaxies arethe remains of a compact group of galaxies that have completely merged.
| Ultraluminous X-ray source populations in normal galaxies: a preliminary survey with Chandra
We present results of a Chandra survey of the ultraluminous X-raysources (ULX) in 13 normal galaxies, in which we combine sourcedetection with X-ray flux measurement. 22 ULX were detected, i.e. withLx > 1 × 1039 erg s-1(L10) and 39 other sources were detected with Lx> 5 × 1038 erg s-1 (L5). Wealso use radial intensity profiles to remove extended sources from thesample. The majority of sources are not extended, which for a typicaldistance constrains the emission region size to less than 50 pc. X-raycolour-colour diagrams and spectral fitting results were examined forindicators of the ULX nature. In the case of the brighter sources,spectral fitting generally requires two-component models. In only a fewcases do colour-colour diagrams or spectral fitting provide evidence ofa black hole nature. We find no evidence of a correlation with stellarmass, however, there is a strong correlation with star formation asindicated by the 60-μm flux as found in previous studies.
| Redshift-Distance Survey of Early-Type Galaxies: Spectroscopic Data
We present central velocity dispersions and Mg2 line indicesfor an all-sky sample of ~1178 elliptical and S0 galaxies, of which 984had no previous measures. This sample contains the largest set ofhomogeneous spectroscopic data for a uniform sample of ellipticalgalaxies in the nearby universe. These galaxies were observed as part ofthe ENEAR project, designed to study the peculiar motions and internalproperties of the local early-type galaxies. Using 523 repeatedobservations of 317 galaxies obtained during different runs, the dataare brought to a common zero point. These multiple observations, takenduring the many runs and different instrumental setups employed for thisproject, are used to derive statistical corrections to the data and arefound to be relatively small, typically <~5% of the velocitydispersion and 0.01 mag in the Mg2 line strength. Typicalerrors are about 8% in velocity dispersion and 0.01 mag inMg2, in good agreement with values published elsewhere.
| Chandra Observations of the Interacting NGC 4410 Galaxy Group
We present high-resolution X-ray imaging data from the ACIS-S instrumenton the Chandra telescope of the nearby interacting galaxy group NGC4410. Four galaxies in the inner portion of this group are clearlydetected by Chandra, including the peculiar low-luminosity radio galaxyNGC 4410A. In addition to a nuclear point source, NGC 4410A containsdiffuse X-ray emission, including an X-ray ridge extending out to about12" (6 kpc) to the northwest of the nucleus. This ridge is coincidentwith an arc of optical emission-line gas, which has previously beenshown to have optical line ratios consistent with shock ionization. Thisstructure may be due to an expanding superbubble of hot gas caused bysupernovae and stellar winds or by the active nucleus. The Chandraobservations also show four or five possible compact ultraluminous X-ray(ULX) sources (LX>=1039 ergs s-1)associated with NGC 4410A. At least one of these candidate ULXs appearsto have a radio counterpart, suggesting that it may be due to an X-raybinary with a stellar-mass black hole, rather than an intermediate-massblack hole. In addition, a faint diffuse intragroup X-ray component hasbeen detected between the galaxies (LX~1041 ergss-1). This supports the hypothesis that the NGC 4410 group isin the process of evolving via mergers from a spiral-dominated group(which typically has no X-ray-emitting intragroup gas) to anelliptical-dominated group (which often has a substantial intragroupmedium).
| Small-Scale Systems of Galaxies. I. Photometric and Spectroscopic Properties of Members
This paper is the first of a series addressed to the investigation ofgalaxy formation/evolution in small-scale systems of galaxies (SSSGs),which are located in low-density cosmic environments. Our algorithm forSSSG selection includes galaxy systems of two or more galaxies lyingwithin Δcz<=1000 km s-1 and a 200h-1100 kpc radius volume. We present the analysisof the photometric and spectroscopic properties of 19 member galaxiesbelonging to a sample of 11 SSSGs. In the μe-replane early-type members may be considered ``ordinary,'' rather than``bright,'' galaxies, with a significant fraction of galaxies having adisk or disky isophotes. We do not detect fine structure or signaturesof recent interaction events in the early-type galaxy population, apicture also confirmed by the spectroscopy. At odds with these findingsare several spiral members with open arm configurations, as expected ininteracting systems. At the same time, emission lines in the spectra ofspiral members fall in the H II regions regime. None of the objectsdisplays unambiguous indications of nuclear activity, although fourspiral nuclei could be ascribed to the class of Seyferts. The starformation rate seems enhanced over the average expected in spiralgalaxies only for poorer SSSGs in particular pairs (<=50Msolar yr-1) but without being in the range ofstarburst systems.Based on observations obtained at the European Southern Observatory, LaSilla, Chile (program No. 57.B-036).
| Redshift-Distance Survey of Early-Type Galaxies: Circular-Aperture Photometry
We present R-band CCD photometry for 1332 early-type galaxies, observedas part of the ENEAR survey of peculiar motions using early-typegalaxies in the nearby universe. Circular apertures are used to tracethe surface brightness profiles, which are then fitted by atwo-component bulge-disk model. From the fits, we obtain the structuralparameters required to estimate galaxy distances using theDn-σ and fundamental plane relations. We find thatabout 12% of the galaxies are well represented by a pure r1/4law, while 87% are best fitted by a two-component model. There are 356repeated observations of 257 galaxies obtained during different runsthat are used to derive statistical corrections and bring the data to acommon system. We also use these repeated observations to estimate ourinternal errors. The accuracy of our measurements are tested by thecomparison of 354 galaxies in common with other authors. Typical errorsin our measurements are 0.011 dex for logDn, 0.064 dex forlogre, 0.086 mag arcsec-2 for<μe>, and 0.09 for mRC,comparable to those estimated by other authors. The photometric datareported here represent one of the largest high-quality and uniformall-sky samples currently available for early-type galaxies in thenearby universe, especially suitable for peculiar motion studies.Based on observations at Cerro Tololo Inter-American Observatory (CTIO),National Optical Astronomy Observatory, which is operated by theAssociation of Universities for Research in Astronomy, Inc., undercooperative agreement with the National Science Foundation (NSF);European Southern Observatory (ESO); Fred Lawrence Whipple Observatory(FLWO); and the MDM Observatory on Kitt Peak.
| A new catalogue of ISM content of normal galaxies
We have compiled a catalogue of the gas content for a sample of 1916galaxies, considered to be a fair representation of ``normality''. Thedefinition of a ``normal'' galaxy adopted in this work implies that wehave purposely excluded from the catalogue galaxies having distortedmorphology (such as interaction bridges, tails or lopsidedness) and/orany signature of peculiar kinematics (such as polar rings,counterrotating disks or other decoupled components). In contrast, wehave included systems hosting active galactic nuclei (AGN) in thecatalogue. This catalogue revises previous compendia on the ISM contentof galaxies published by \citet{bregman} and \citet{casoli}, andcompiles data available in the literature from several small samples ofgalaxies. Masses for warm dust, atomic and molecular gas, as well asX-ray luminosities have been converted to a uniform distance scale takenfrom the Catalogue of Principal Galaxies (PGC). We have used twodifferent normalization factors to explore the variation of the gascontent along the Hubble sequence: the blue luminosity (LB)and the square of linear diameter (D225). Ourcatalogue significantly improves the statistics of previous referencecatalogues and can be used in future studies to define a template ISMcontent for ``normal'' galaxies along the Hubble sequence. The cataloguecan be accessed on-line and is also available at the Centre desDonnées Stellaires (CDS).The catalogue is available in electronic form athttp://dipastro.pd.astro.it/galletta/ismcat and at the CDS via anonymousftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via\http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/405/5
| The ROSAT All-Sky Survey: a Catalog of Clusters of Galaxies in a Region of 1 steradian around the South Galactic Pole
A field of 1.013 sr in the ROSAT All-Sky Survey (RASS), centered on thesouth Galactic pole (SGP), has been searched in a systematic, objectivemanner for clusters of galaxies. The procedure relied on a correlationof the X-ray positions and properties of ROSAT sources in the field withthe distribution of galaxies in the COSMOS digitized database, which wasobtained from scanning the plates of the UK Schmidt IIIa-J opticalsurvey of the southern sky. The study used the second ROSAT surveydatabase (RASS-2) and included several optical observing campaigns tomeasure cluster redshifts. The search, which is a precursor to thelarger REFLEX survey encompassing the whole southern sky, reached thedetection limits of both the RASS and the COSMOS data and yielded acatalog of 186 clusters in which the lowest flux is1.5×10-12 ergs cm-2 s-1 in the0.1-2.4 keV band. Of these 157 have measured redshifts. Using a fluxlimit of 3.0×10-12 ergs cm-2 s-1a complete subset of 112 clusters was obtained, of which 110 havemeasured redshifts. The spatial distribution of the X-ray clusters outto a redshift of 0.15 shows an extension of the Local Supercluster tothe Pisces-Cetus supercluster (z<~0.07), and an orthogonal structureat higher redshift (0.07
| Revisiting Brightest Cluster Galaxy Evolution with the Las Campanas Distant Cluster Survey
We investigate the influence of environment on brightest cluster galaxy(BCG) evolution using a sample of 63 clusters at 0.3<=z<=0.9 drawnprimarily from the Las Campanas Distant Cluster Survey and follow-up V,I, and K' photometry. The luminosity evolution of the entire BCG sampleis not adequately described by a single evolutionary model. Using theintegrated light from the cluster detection as a proxy for clusterLX and the suggestion by Burke, Collins, & Mann, we setLX=2×1044 ergs s-1 to be thedivision between high- and low-luminosity clusters. At high redshift(z>0.6) BCGs from low-LX clusters are fainter, on average,than those from high-LX clusters and are best modeled ashaving constant luminosity with redshift. The BCGs fromhigh-LX clusters are best modeled as having a stellarpopulation that formed at large redshift (zform>5) and ispassively evolving. However, for the entire BCG population, the observedV-I and I-K' colors are well described by a single evolutionary model inwhich the stellar populations have zform>5 andsubsequently passively evolve. We conclude that accretion isproportionally more significant for BCGs in lower mass clusters at theseredshifts (a factor of 2-4 increase in mass since z~1 for thelow-LX systems; Aragon-Salamanca and coworkers) and that theaccreted matter is in the form of systems with evolved stellarpopulations.
| The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
| X-ray luminosities of galaxies in groups
We have derived the X-ray luminosities of a sample of galaxies ingroups, making careful allowance for contaminating intragroup emission.The LX:LB and LX:LFIRrelations of spiral galaxies in groups appear to be indistinguishablefrom those in other environments, however the elliptical galaxies fallinto two distinct classes. The first class is central-dominant groupgalaxies, which are very X-ray luminous and may be the focus of groupcooling flows. All other early-type galaxies in groups belong to thesecond class, which populates an almost constant band ofLX/LB over the range9.8
| Soft X-ray Properties of Ultraluminous IRAS Galaxies
We report on the results of cross-correlation of a sample of 903Ultraluminous IRAS galaxies (ULIRGs) with the ROSAT-All Sky SurveyBright Source Catalogue and the ROSAT archived pointing observations.The sample of ULIRGs has been compiled from the recently released PSCzredshift survey. In total, 35 ULIRGs are securely detected by the ROSATAll-Sky Survey and pointing observations, five of which are blazars. Thestatistical properties of these sources in the soft X-ray band aredetermined and compared with their properties in other wavebands. Wefind that the ratio of the soft X-ray to the far-infrared flux spansabout five orders of magnitude and reaches values of about unity. Thisratio is a good indicator of the main energy source of ULIRGs. Thosewith soft X-ray to far-infrared flux exceeding 0.01 are probably poweredby accretion onto central supermassive black holes while those withratios smaller than 0.001 are probably powered by starbursts or otherheating processes, or are Compton thick sources. Some ULIRGs have energycontributions from both. This ratio is low for most ULIRGs andhyperluminous infrared galaxies, which explains their low detection rateby ROSAT and ASCA. We also find that some ULIRGs have a similar softX-ray luminosity vs. temperature relation to that for groups of galaxiesand elliptical galaxies, suggesting a common origin of these systems.Our study also reveals a tight correlation between the hardness ratioand the soft X-ray luminosity for Seyfert 1s/QSOs.
| The Optical and Near-Infrared Morphologies of Isolated Early-Type Galaxies
To study early-type galaxies in their simplest environments, we haveconstructed a well-defined sample of 30 isolated galaxies. The samplecontains all early-type galaxies listed in the Third Reference Catalogueof Bright Galaxies (RC3) with no other cataloged galaxy with a knownredshift lying within a projected radius of 1h-1100 Mpc and +/-1000 km s-1 (where weuse the recession velocities in the RC3). We have obtained optical andnear-infrared images of 23 of the galaxies and of a comparison sample of13 early-type galaxies in X-ray-detected poor groups of galaxies. Wehave applied the techniques of unsharp-masking, galaxy model division,and color maps to search for morphological features that might provideclues to the evolution of these galaxies. Evidence for dust features isfound in approximately 75% of both the isolated and group galaxies (17of 22 and 9 of 12, respectively). However, shells or tidal features aremuch more prevalent in our isolated sample than in our group sample (9of 22=41% vs. 1 of 12=8%, respectively). The isolation and colors ofthese shell galaxies make it unlikely that tidal interactions orasymmetric star formation are the causes of such features. One modelthat is not ruled out is that mergers produce the shells. If shells anddust are both merger signatures, the absence of shells in groupelliptical galaxies implies that shells (1) form more easily, (2) areyounger, and/or (3) are longer lived in isolated environments.
| The Dwarf Galaxy Population of the Dorado Group Down to MV~-11
We present V and I CCD photometry of suspected low surface brightnessdwarf galaxies detected in a survey covering ~2.4 deg2 aroundthe central region of the Dorado group of galaxies. The low surfacebrightness galaxies were chosen based on their sizes and magnitudes atthe limiting isophote of 26 Vμ. The selected galaxies have magnitudesbrighter than V~20 (MV~-11 for an assumed distance to thegroup of 17.2 Mpc), with central surface brightnessesμ0>22.5 V mag arcsec-2, scale lengths h>2", anddiameters >=14" at the limiting isophote. Using these criteria, weidentified 69 dwarf galaxy candidates. Four of them are large very lowsurface brightness galaxies that were detected on a smoothed image,after masking high surface brightness objects. Monte Carlo simulationsperformed to estimate completeness, photometric uncertainties and toevaluate our ability to detect extended low surface brightness galaxiesshow that the completeness fraction is, on average, >80% for dwarfgalaxies with -17=14"). The V-I colors of the dwarfcandidates vary from -0.3 to 2.3 with a peak on V-I=0.98, suggesting arange of different stellar populations in these galaxies. The projectedsurface density of the dwarf galaxies shows a concentration toward thegroup center similar in extent to that found around five X-ray groupsand the elliptical galaxy NGC 1132 studied by Mulchaey & Zabludoff,suggesting that the dwarf galaxies in Dorado are probably physicallyassociated with the overall potential well of the group. Based on thedata collected at the Cerro Tololo Inter-American Observatory (CTIO) andLas Campanas Observatory, Chile.
| X-ray evidence for multiphase hot gas with nearly solar Fe abundances in the brightest groups of galaxies
We analyse the ASCA spectra accumulated within ~100kpc radii of 12 ofthe brightest groups of galaxies. Upon fitting isothermal models (1T)jointly to the ASCA SIS and GIS spectra we obtain fits for most groupsthat are of poor or at best marginal quality and give very subsolarmetallicities similar to previous studies,=0.29+/-0.12Zsolar. Two-temperature models (2T)provide significantly better fits for 11 out of the 12 groups, and inevery case have metallicities that are substantially larger thanobtained for the 1T models, =0.75+/-0.24Zsolar.Though not very well constrained, for most of the groups absorption inexcess of the Galactic value is indicated for the cooler temperaturecomponent of the 2T models. A simple multiphase cooling flow model givesresults analogous to the 2T models including large metallicities,=0.65+/-0.17Zsolar. The nearly solar Fe abundancesand also solar α/Fe ratios indicated by the 2T and cooling flowmodels are consistent with models of the chemical enrichment ofellipticals, groups, and clusters which assume ratios of Type Ia to TypeII supernovae and an initial mass function (IMF) similar to those of theMilky Way. Thus we have shown that the very subsolar Fe abundances andSi/Fe enhancements obtained from most previous studies within r~100kpcof galaxy groups are an artefact of fitting isothermal models to theX-ray spectra, which also has been recently demonstrated for thebrightest elliptical galaxies. Owing to the importance of these resultsfor interpreting X-ray spectra, in an appendix we use simulated ASCAobservations to examine in detail the `Fe bias' and `Si bias' associatedwith the spectral fitting of ellipticals, groups and clusters ofgalaxies.
| X-ray Properties of Groups of Galaxies
ROSAT observations indicate that approximately half of all nearby groupsof galaxies contain spatially extended X-ray emission. The radial extentof the X-ray emission is typically 50-500 h-1100kpc or approximately 10-50% of the virial radius of the group. DiffuseX-ray emission is generally restricted to groups that contain at leastone early-type galaxy. X-ray spectroscopy suggests the emissionmechanism is most likely a combination of thermal bremsstrahlung andline emission. This interpretation requires that the entire volume ofgroups be filled with a hot, low-density gas known as the intragroupmedium. ROSAT and ASCA observations indicate that the temperature of thediffuse gas in groups ranges from approximately 0.3 keV to 2 keV. Highertemperature groups tend to follow the correlations found for richclusters between X-ray luminosity, temperature, and velocity dispersion.However, groups with temperatures below approximately 1 keV appear tofall off the cluster LX-T relationship (and possibly theLX-σ and σ-T cluster relationships, althoughevidence for these latter departures is at the present time not verystrong). Deviations from the cluster LX-T relationship areconsistent with preheating of the intragroup medium by an earlygeneration of stars and supernovae. There is now considerable evidencethat most X-ray groups are real, physical systems and not chancesuperpositions or large-scale filaments viewed edge-on. Assuming theintragroup gas is in hydrostatic equilibrium, X-ray observations can beused to estimate the masses of individual systems. ROSAT observationsindicate that the typical mass of an X-ray group is ~ 1013h-1100 Msolar out to the radius towhich X-ray emission is currently detected. The observed baryonic massesof groups are a small fraction of the X-ray determined masses, whichimplies that groups are dominated by dark matter. On scales of thevirial radius, the dominant baryonic component in groups is likely theintragroup medium.
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